1. Field of the Invention
The present invention relates to a radiation imaging apparatus, a method of driving the same, and a radiation inspection apparatus.
2. Description of the Related Art
A radiation imaging apparatus (to be simply referred to as an “imaging apparatus” hereinafter) includes a plurality of sensors, and obtains image data representing the internal information of an object based on the radiation passing through the object and detected by a plurality of sensors.
Japanese Patent Laid-Open No. 2002-344809 discloses an example of the arrangement of sensors. Each sensor shown in FIG. 10 in Japanese Patent Laid-Open No. 2002-344809 includes a detection element which detects radiation, a first reset unit which resets the detection element, a clamp unit which clamps a signal from the detection element when it is reset by the first reset unit, and a second reset unit which resets the clamp unit. This sensor also includes a first sampling unit which samples, as an optical signal (S signal), the voltage of the clamp unit which has received a signal from the detection element which has detected radiation after it is reset by the first reset unit. The sensor further includes a second sampling unit which samples, as a noise signal (N signal), the voltage of the clamp unit when it is reset by the second reset unit.
This arrangement makes it possible to remove fixed pattern noise caused by the sensor arrangement or the like while removing kTC noise caused by heat or the like from the signal obtained by a sensor.
When performing movie image capturing, the imaging apparatus can obtain a plurality of image data by repeatedly reading out signals from a plurality of sensors, and output the plurality of image data to a display or the like in the order in which they were obtained. The time required to obtain one image data by performing signal readout from a plurality of sensors once is also called a frame rate.
Movie image capturing requires a technique of changing (greatly or slightly) the frame rate while performing capturing in accordance with the observation target region of an object, the observation method or the like to be used, and the purpose. For example, increasing the frame rate makes it possible to smoothly play back a movie image because a plurality of image data are obtained at short intervals. Decreasing the frame rate makes it possible to improve the sensor sensitivity because it is possible to increase the accumulation time of charges in each detection element. For example, the frame rate may be increased when observing the movement of an observation target region, and may be decreased when observing an affected area of the region in detail.